Process for chemically watermarking paper and product thereof



United States Patent f 3,288,628 PROCESS FOR CHEMICALLY WATERMARKING PAPER AND PRODUCT THEREOF Milton 0. Schur, New Haven, Conn., and John H. Goldberger, Brevard, N.C., assignors to Olin Mathieson Chemical Corporation, New Haven, Conn, 21 corporation of Virginia No Drawing. Filed Oct. 1, 1962, Ser. No. 227,578

Claims. (Cl. 11738) This invention relates to the application to printable paper sheets of impregnated translucent identification marks, characterized as substantially permanent and not imp-airing the printing and writing properties of the paper surface. In addition to other advantages, this invention enables the accurate placing of translucent marks at the same desired location on successive cut paper sheets by a printing or stamping operation carried out with the use of suitable compositions.

C-ut paper sheets provided with the conventional type of watermark, applied during the paperm-aking process, generally carry the watermarked monogram or design at random locations. The accurate placing in cut sheets of watermarks applied by the conventional process would necessarily involve unusual precautions and an increased proportion of scrap, and is therefore unduly expensive.

Compositions have been known for impregnation of paper for increasing the transparency thereof and result in translucent sheets or in sheets having translucent areas. However, such compositions tend to migrate laterally through the paper sheet. Attempts to apply designs or marks on paper by printing such compositions have been unsuccessful because of one or more of the following disadvantages: fuzziness of the impressed design or mark because of lateral spreading, lack of permanence, and altering the surface so that it does not readily receive print or writing.

The principal object of this invention has therefore been to overcome the above disadvantages by providing suitable compositions which may be printed or stamped on paper to result in well-defined marks or designs imparting permanent translucency at the desired location, the surface areas of which retain the capacity of the untreated portions of the paper to receive writing or printing impressions.

The foregoing and other objectives have been attained in accordance with this invention by printing or stamping designs or marks on paper with the use of liquid compositions including two substantially non-volatile ingredi'ents of suitable structure and properties to penetrate readily from one paper surface to the other, without substantial lateral migration, and to be retained permanently by the impregnated cellulose fibers.

The main ingredient is an organic ester or polyester, of molecular weight of about 300 to 10,000 which at room temperature or at :a temperature not higher than about 65 C. exists as a viscous liquid, for example, having a viscosity exceeding about 1,000 poises. Linear polyesters of glycols with aliphatic dicarboxylic acids are efiective, and particularly the linear polyesters, or mixtures thereof, of glycols having 2 to 4 carbon atoms (ethylene, propylene and butylene glycols) with the aliphatic dicarboxylic acids containing 6 to 10 carbon atoms (adipic, pimelic, suberic, azelaic and sebacic acids). Hydrogenated abietate esters with ethylene glycol, diethylene glycol or triethylene glycol, or mixtures thereof are likewise suit-able, particularly the triethylene glycol ester. This first ingredient constitutes 55 to 90% by weight of the residual fiber impregnating material.

Useful compositions must also include 10 to 45% by weight of a non-volatile monomeric organic ester plasticizer, which has a melting point below about 45 C. and

3,288,628 Patented Nov. 29, 1966 has a boiling point over 250 C. Highly efi'ective esters are the glycerol esters of the lower fatty acids, particularly glycerol triacetate and glycerol tripropionate, and the esters of abietic acid and of stearic acid with the lower monohydric alcohol containing 1 to 8 carbon atoms, particularly the methyl and ethyl esters thereof. Diesters of phthalic acid with the lower monohydric alcohols are likewise suitable, particularly the dimethyl, diethyl, dipropyl, dibutyl, dicyclohexyl and dioctyl phthalates, generally in lower proportions not exceeding about 25% by weight because of their high fluidity.

The combination of the high molecular weight ester and the monomeric ester plasticizer results in a liquid of suitable fluidity and polarity to accomplish rapid penetration through the web of paper sheets without lateral spreading. At the same time, suflicient forces of attraction exist between the liquid esters and cellulose so that the impregnated fibers tend to be stable and substantially permanent.

It is at times convenient to replace a portion, up to about a half, of the plasticizer component by a polar volatile organic solvent such as a lower alcohol, ether or ketone or mixture thereof,-including methyl, ethyl, propyl or isopropyl alcohol, diethyl ether, acetone, or methyl ethyl ketone.

The following specific examples in accordance with the invention constitute preferred illustrative compositions, the listed proportions being by weight.

In examples as above, the liquid ester component may consist of Paraplex 6-40 (Rohm & Haas), of Staybelite Ester No. 3 (Hercules Powder 00.), or of Polyethylene Glycol 400 Distearate (Glyco Products Co). The plasticizer of Examples 3 and 4 may consist of Hercolyn (Hercules Powder 00.).

Monograms, numerals or other marks or designs are readily applied using compositions as described above at the desired location on paper sheets by conventional stamping or printing methods, for example by letter press or offset printing. The edges of the marks or designs are sharp and well defined and the mark or design is uniformly translucent and clearly visible when the sheet is viewed by transmitted light or by reflected light, when the sheet is placed upon a dark background. Also, the

surface properties of the marked sheet with respect to receiving writing or printing are not impaired, writing and printing inks being received uniformly as intended, without diffusion beyond the desired area. Furthermore, paper sheets impressed with translucent marks or'designs produced in accordance with this invention retain such well-defined marks or designs even after accelerated storage tests, for example, after heating in air for 16 hours at C. In sheets carrying printed text over the impressed mark, both the mark and the text are nonfugitive and color-stable after accelerated tests, as above.

It is noteworthy that one or more of the above requirements is not obtainable with the prior art compositions, such as have been proposed for the transparentizing of paper. For the most part, such compositions difiuse laterally beyond the line of application and thus result in printed designs having indistinct and fuzzy edges. In accelerated tests, the rate of lateral diffusion is increased so that the design or mark practically dis-appears. With the use of non-polar or slightly polar compounds such as paraffin, petrolatum, stearic acid and similar compounds, the surface properties are altered so that writing and printing inks are not uniformly received. Highly polar compounds are disadvantageous in being sufficiently hygroscopic to cause localized swelling and puckering of the paper sheet or to efiect undesirable spreading of subsequently applied writing or printing inks.

In applying marks or designs in accordance with the invention, it is essential to avoid compositions containing appreciable proportions of volatile solvent beyond about 30% by weight. The use of higher percentages of volatile solvent tends to promote the lateral spreading of the composition to an undesirable extent and after volatilization leads to the formation of voids within the impregnated area and imparts a mottled appearance and impaired distinctness of the design or mark.

Modifications of the above-described illustrative 'ernbodiments will be obvious to those skilled in the art, without departing from the spirit and scope of the invention, as defined in the claims.

What is claimed is:

1. The process of marking paper sheets with a permanent colorless translucent design comprising printing on paper sheets a layer of liquid in the shape of the said design, which layer is adapted to penetrate rapidly the web of said sheets substantially without lateral diffusion beyond the periphery of the said design, said liquid consisting essential-1y of 55 to 90 percent by weight of liquid organic viscous ester having a molecular weight in the range of about 300 to 10,000 and to 45 percent by weight of a monomeric non-volatile liquid organic ester plasticizer having a melting point below 45 C. and a boiling point over 250 C.

2. The process of claim 1, wherein the said viscous ester is a linear polyester of a glycol having 2 to 4 carbon atoms with an aliphatic dicarboxylic acid having 6 to 10 carbon atoms.

3. The process of claim 1, wherein the said ester plasticizer is a glycerol ester of a lower fatty acid.

4. The process of claim 1, wherein the said ester plasticizer is a lower monohydric alcohol ester ofan acid selected from the group consisting of abietic, phthalic and stearic acids.

5.- The process of claim 1, wherein the said viscous ester is polypropylene .adipate and the said ester plasticizer is glycerol triacetate.

6. A paper sheet having a substantially permanent colorless translucent design impregnated in the web thereof, said web being impregnated within the periphery of said design with .a liquid composition consisting essentially of to 90 percent by weight of a liquid organic viscous ester having a molecular weight in the range of about 300 to 10,000 and 10 to 45 percent by weight of a monomeric non-volatile liquid organic ester plasticizer having a melting point below 45 C. and a boiling point over 250 C.

7. A paper sheet in accordance with claim 6, wherein the said viscous ester is a linear polyester of a glycol having 2 to 4 carbon atoms with an aliphatic dicarboxylic acid having 6 to 10 carbon atoms.

8. A paper sheet in accordance with claim 6, wherein the said ester plasticizer is a glycerol ester of a lower fatty acid.

9. A paper sheet in accordance with claim 6, wherein the said ester plasticizer is a lower monohydric alcohol ester of an acid selected from the group consisting of abietic, pht-halic and stearic acids.

10. A paper sheet in accordance with claim 6, wherein the said viscous ester is polypropylene adipate and the said ester plasticizer is glycerol triacetate.

References Cited by the Examiner UNITED STATES PATENTS 2,611,756 9/1952 Pockel 260-22 X 2,749,329 6/1956 Ludlow 260- 3,140,959 7/1964 Vaurio 1l738 MURRAY KATZ, Primary Examiner.

H. W. MYLIUS, Assistant Examiner. 

1. THE PROCESS OF MARKETING PAPER SHEETS WITH A PERMANENT COLORLESS TRANSLUCENT DESIGN COMPRISING PRINTING ON PAPER SHEETS A LAYER OF LIQUID IN THE SHAPE OF THE SAID DESIGN, WHICH LAYER IS ADAPTED TO PENETRATE RAPIDLY THE WEB OF SAID SHEETS SUBSTANTIALLY WITHOUT LATERAL DIFFUSION BEYOND THE PERIPHERY OF THE SAID DESIGN, SAID LIQUID CON SISTING ESSENTIALLY OF 55 TO 90 PERCENT BY WEIGHT OF LIQUID ORGANIC VISCOUS ESTER HAVING A MOLECULAR WEIGHT IN THE RANGE OF ABOUT 300 TO 10,000 AND 10 45 PERCENT BY WEIGHT OF A MONOMERIC NON-VOLATILE LIQUID ORGANIC ESTER PLASTICIZER HAVING A MELTING POINT BELOW 45*C. AND A BOILING POINT OVER 250*C. 